1. Field of the Invention
This invention relates to elastomers synthesized from crude C.sub.5 -hydrocarbons, preferably crude C.sub.5 -hydrocarbon mixtures which are by-products in the production of ethylene. A selected portion of the crude C.sub.5 -hydrocarbons are copolymerized in the presence of a catalyst system to prepare an elastomer having the requisite properties to produce a pressure sensitive adhesive when added to a natural or synthetic tackifier.
In recent years many petrochemical companies have become increasingly interested in the utilization of by-products from petrochemical operations, for example, ethylene plants because of the increased availability and lower costs of these hydrocarbons as compared with their polymer grade counterparts. It has now been discovered that an elastomer synthesized from crude C.sub.5 -hydrocarbons, when used in combination with natural or synthetic tackifiers, is particularly suited for use as pressure-sensitive adhesives. This is very encouraging in view of existing natural resin shortages and the fact that the adhesives industry is placing increased emphasis on adhesives containing tackifiers of synthetic origin. The elastomers as defined herein have improved characteristics such as tack and peel strength when compounded with tackifiers to provide the required pressure-sensitive adhesive properties. The concurrently filed application of Lakshmanan et al., entitled "Pressure-Sensitive Adhesive Composition," Ser. No. 755,160 filed Dec. 29, 1976, describes suitable applications and adhesive compositions containing the elastomers herein, the disclosure of which is incorporated herein by reference.
2. Description of the Prior Art
The catalytic polymerization of C.sub.5 -hydrocarbons to form a resinous compound is known. For example, U.S. Pat. No. 3,793,261 issued to Katayama et al., on Feb. 19, 1974, entitled "Process for Preparing Petroleum Resin", discloses a process which is described as suitable for preparing petroleum resins having improved tackiness in rubber applications. In particular, the starting material for the resinous product comprises a by-product fraction in petroleum refining composed primarily of unsaturated hydrocarbons containing 5 carbon atoms. Included among the hydrocarbon by-product are 1-pentene, 2-pentene, isoprene, 1,3-pentadiene, cyclopentadiene and the like. In some cases these hydrocarbons have been obtained from cracked naphthas, as for example, in U.S. Pat. No. 2,719,853 and 2,773,838 to Reid et al..
Another process relating to the separation of C.sub.5 -hydrocarbons distilled from a cracked petroleum fraction and use of the resulting product is disclosed in U.S. Pat. No. 3,865,797 issued to Joy, on Feb. 11, 1975, entitleld "Process for the Production of Petroleum Resins of Varying Softening Points". The reference teaches a petroleum resin feedstock which comprises C.sub. 5 -hydrocarbons distilled from a cracked petroleum fraction in combination with a butadiene raffinate consisting of isobutene, 1-butene, 2-butene and butanes.
As can be determined from the above, there have been many processes and applications directed to the use of C.sub.5 -hydrocarbons derived from a cracked petroleum fraction. There is, however, an ongoing search for new and different uses for this petroleum product which is usually described as a by-product in the production of petroleum compositions.